Mckelveyite - Encyclopedia
Class : Carbonates, nitrates, borates
Subclass : Hydrated carbonates
Crystal system : Triclinic
Chemistry : Ba3Na(Ca,U)(Y,Nd)(CO3)6 3H2O
Rarity : Very rare
Mckelveyite is a group of two carbonates, from nepheline syenites and carbonatites, which form a series between the yttrium pole mckelveyite-(Y) and the neodymium pole mckelveyite-(Nd). Its name was given in honor of Vincent Ellis McKelvey, Director of the US Geological Survey. We know relatively little about this extremely rare mineral ; it forms small pseudohexagonal crystals in barrels of 3 cm maximum, and pseudorhombohedral discoid crystals of 3 mm in veins of calcite and natrolite. Its crystals can also be lamellar. Its colors vary : white, green, gray of different tones, yellow to brown, sometimes black.
Main photo : Mcguinnessite from Lobminggraben, Styria, Austria © Christian Auer
Mckelveyite in the World
Twinning
No twin known for this mineral species.
Fakes and treatments
No fakes recorded for this mineral species.
Hardness : 3.5 to 4
Density : 3.25
Fracture : Irregular
Streak : White
TP : Transparent to opaque
RI : 1.550 to 1.658
Birefringence : 0.099 to 0.104
Optical character : Biaxial -
Pleochroism : Visible
Fluorescence : None
Solubility : -
Magnetism : NoneRadioactivity : Medium